Toxic unit
Toxic units (TU) are used in the field of toxicology to quantify the interactions of toxicants in binary mixtures of chemicals. A toxic unit for a given compound is based on the concentration at which there is a 50% effect (ex. EC50) for a certain biological endpoint. One toxic unit is equal to the EC50 for a given endpoint for a specific biological effect over a given amount of time. Toxic units allow for the comparison of the individual toxicities of a binary mixture to the combined toxicity. This allows researchers to categorize mixtures as additive, synergistic or antagonistic. Synergism and antagonism are defined by mixtures that are more or less toxic than predicted by the sum of their toxic units. Contaminants are frequently present as mixtures in the environment. Regulatory decisions are based on mixture toxicity models that assume additivity, which can result in under or overestimation of toxic effects. Refining our understanding of mixture interactions can lead to better informed environmental management and decision making. In addition, exploring mixture interactions can elucidate the mechanisms of action for specific toxicants which, in many cases, are poorly understood. (Wikipedia).
